The present invention relates generally to vibration-damping, and more particularly to an improvement to a vibration-damping structural component of the type having viscoelastic material sandwiched between two outer structural layers of stiffness material.
Various load-bearing systems and structures, such as aircraft, experience vibrations during use which cause them to suffer from high-cycle and resonant fatigue and reduced service life. One means for reducing such vibrations is to use viscoelastic material, which converts vibrations into heat when strained. Often a free layer of viscoelastic material is fixed to the surface of the base structure. When the base structure is subjected to bending or flexural loads, the viscoelastic layer strains in tension and compression. An additional stiffness layer may also be fixed to the outer surface of the viscoelastic layer as a constraining layer. Under these circumstances, the bending or flexural loads deform the structure and the constraining layer, loading the viscoelastic material in shear, a more effective damping mode for viscoelastic materials.
Another approach to damping vibrations is to construct the structure itself from a vibration-damping laminated composite having two constraining layers of stiffness material and a damping layer of viscoelastic material sandwiched therebetween. Under bending loads the viscoelastic layer is loaded in shear to absorb the vibrational energy. Most of the shear of the viscoelastic layer occurs at the ends of the mode shapes of the dominant vibrational mode. At the peaks of the mode shape for the dominant mode there are "dead" areas of viscoelastic material which do not shear at all. Since maximum vibration damping takes place when maximum shearing occurs in the viscoelastic material, it is desirable to increase the rate or amount of shear straining therein.